1 62 POPULAR SCIENCE MONTHLY. 



and magnetic force, which are sent out from a certain radiating center, 

 and in order to localize that center we have to determine the position 

 of the plane of the wave and also the curvature of the surface at the 

 receiving point. Something therefore equivalent to a range-finder 

 in connection with light is necessary to enable us to locate the distance 

 and the direction of the radiant point. 



Lastly, there are important improvements possible in connection 

 with the generation of the waves themselves. At the present moment, 

 our mode of generating Hertzian waves involves a dissipation of energy 

 in the form of the light and heat of the spark. Just as in the case of 

 ordinary artificial illuminants, such as lamps of various kinds, we have 

 to manufacture a large amount of ether radiation of long wave length, 

 which is of no use to us for visual purposes; in fact, creating ninety- 

 five per cent, of dark and useless waves for every five per cent, of 

 luminous or useful waves, so in connection with present methods of 

 generating Hertzian waves, we are bound to manufacture by the dis- 

 charge spark a large amount of light and heat rays which are not 

 wanted, in order to create the Hertzian waves we desire. It is impos- 

 sible yet to state precisely what is the efficiency, in the ordinary sense 

 of the word, of a Hertzian wave radiator. How much of the energy 

 imparted to the aerial falls back upon it and contributes to the pro- 

 duction of the spark, and how much is discharged into the ether in the 

 form of a wave. 



Nothing is more remarkable, however, than the small amount of 

 energy which, if properly utilized in electric wave making, will suffice 

 to influence a sensitive receiver at a distance of even one or two hun- 

 dred miles. Suppose, for instance, that we charge a condenser con- 

 sisting of a battery of Leyden jars, having a capacity of one seventy- 

 fifth of a microfarad, to a potential of 15,000 volts; the energy stored 

 up in this condenser is then equal to 1.5 joules, or a little more than 

 one foot-pound. If this energy is discharged in the form of a spark 

 five millimeters in length through the primary coil of an oscillation 

 transformer, associated with an aerial 150 feet in height, the circuits 

 being properly tuned by Mr. Marconi 's method, then such an aerial will 

 affect, as he has shown, one of Mr. Marconi's receivers, including a 

 nickel silver filings coherer tube, at a distance of over two hundred 

 miles over sea. Consider what this means. The energy stored up in 

 the Leyden jars cannot all be radiated as wave energy by the aerial, 

 probably only half of it is thus radiated. Hence the impartation to 

 the ether at any one locality of about half a foot-pound of energy in 

 the form of a long Hertzian wave is sufficient to affect sensitive re- 

 ceivers situated at any point on the circumference of a circle of 200 

 miles radius described on the open sea. Hertzian wave telegraphy is 



